The present invention relates to a method for producing an anti-glare film. More particularly, the present invention relates to a method for producing an anti-glare film for use in the display surface of a display device, such as a liquid crystal display device.
In display devices such as liquid crystal display devices, a technique in which an anti-glare film is formed on the display side and light is diffused by the film to impart anti-glare properties to the display device or to reduce reflection in the surface of the display device is employed. A known anti-glare film imparts anti-glare properties to a display device by virtue of fine irregularities formed in the surface of the film.
FIG. 8 shows the construction of a known anti-glare film 101. The anti-glare film 101 has a substrate 111 and an anti-glare layer 112 formed on the substrate 111. The anti-glare layer 112 includes a resin containing fine particles 113 composed of amorphous silica or resin beads, and the fine particles 113 protrude from the surface of the anti-glare layer 112 to form fine irregularities in the surface. The anti-glare film 101 is formed by applying a coating composition including the fine particles 113, a resin, a solvent, and others to the substrate 111 and drying the coating composition applied.
The method in which a coating composition containing the fine particles 113 is applied to a substrate to produce an anti-glare film is inexpensive and provides good productivity, and whereby the producing method is widely used. However, while the resultant anti-glare film 1 has anti-glare properties, the protrusion shape of the individual fine particles 113, which form surface irregularities of the film, increase the haze value of the surface to cause the image to be whitish, whereby the contrast is lowered and the image definition is also lowered.
The anti-glare film is formed as the uppermost layer on the display side of the liquid crystal display device, and hence is required to have hardness suitable for a hard coat. As a result, it would be desirable to have a thickness as large as several micrometers to several tens micrometers so that an influence of the substrate 111 is not exerted. For forming protrusions of the fine particles 113 in the surface of the anti-glare layer 112 having such a thickness, it would be necessary that fine particles having a particle diameter as large as the thickness of the layer is added. The use of the fine particles having such a large particle diameter causes increasing the appearance of glare (scintillation) on the surface of the anti-glare layer 112, whereby the visibility of the display surface is lowered.
Under the circumstances, as shown in FIG. 9, the packing ratio of the fine particles 113 in the anti-glare layer 112 is reduced to increase the period of the surface irregularities of the anti-glare layer 112, thus improving the contrast. However, in the anti-glare layer 112 having a lengthened period of the surface irregularities to have a moderate irregularities, flat portions are formed between the individual protrusions of the fine particles 113, so that the anti-glare properties of the film become poor.
The anti-glare properties and high contrast are contrary to each other, and it is difficult to achieve both the properties. For achieving both anti-glare properties and high contrast and preventing scintillation, a method in which the surface irregularities of the anti-glare layer are controlled by shape transfer has been proposed.
For example, Japanese Unexamined Patent Application Publication No. 2003-107205 (hereinafter referred to as “Patent Document 1”) discloses a method for producing a shape forming film having desired irregularities using an excimer laser beam processing apparatus. Japanese Unexamined Patent Application Publication No. 2006-154838 (hereinafter referred to as “Patent Document 2”) discloses a method for producing a shape forming film having desired surface irregularities by coating matted polyethylene terephthalate (PET) with a resin. An anti-glare film is produced by, using the shape forming film formed by the above method, transferring desired irregularities to an ultraviolet-curable resin applied onto a substrate, and separating the shape forming film and then curing the resin by ultraviolet irradiation.
However, in the method for forming a shape forming film by laser beam processing described in the patent document 1, the cost of apparatus is high particularly in processing for a large area, e.g., television, and it is difficult to keep high accuracy of processing for the whole area. Further, the production of an anti-glare film by a shape transfer process includes placing an ultraviolet-curable resin in a die and curing the resin and separating the cured resin, and hence the line speed is not easily increased and the mass-productivity is poor.
On the other hand, the method in which a coating composition containing fine particles is applied to a substrate is inexpensive and provides a good productivity as described above, but an anti-glare film having both anti-glare properties and high contrast is difficult to obtain. For solving the problems of contrast or scintillation, the protrusions of fine particles are covered with a resin so that the anti-glare layer has a flat surface, but, in this case, it is difficult to prevent the reflection in the surface of the anti-glare layer, thus reducing the anti-glare properties. In other words, it is difficult to achieve both anti-glare properties and high contrast by controlling the fine irregularities in the surface of the anti-glare layer.